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Impact of Asphalt Thickness on Pavement Quality A Synthesis of Highway Practice Rebecca S. McDaniel North CeNtral Superpave CeNter purdue uNiverSity West Lafayette, IN 2019 Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration Subscriber Categories Highways â¢ Maintenance and Preservation â¢ Pavements N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP SYNTHESIS 537
Published reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet by going to http://www.national-academies.org and then searching for TRB Printed in the United States of America NCHRP SYNTHESIS 537 Project 20-05, Topic 49-05 ISSN 0547-5570 ISBN 978-0-309-48042-0 Library of Congress Control Number 2019942273 Â© 2019 National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FRA, FTA, Office of the Assistant Secretary for Research and Technology, PHMSA, or TDC endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. Cover photo credit: Photo courtesy of Jesse U. Thompson, Jr., South Carolina DOT NOTICE The report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the National Academies of Sciences, Engineering, and Medicine. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; or the program sponsors. The Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturersâ names appear herein solely because they are considered essential to the object of the report. NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transporta- tion results in increasingly complex problems of wide interest to high- way authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 ini- tiated an objective national highway research program using modern scientific techniquesâthe National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine was requested by AASHTO to administer the research program because of TRBâs recognized objectivity and understanding of modern research practices. TRB is uniquely suited for this purpose for many reasons: TRB maintains an extensive com- mittee structure from which authorities on any highway transportation subject may be drawn; TRB possesses avenues of communications and cooperation with federal, state, and local governmental agencies, univer- sities, and industry; TRBâs relationship to the National Academies is an insurance of objectivity; and TRB maintains a full-time staff of special- ists in highway transportation matters to bring the findings of research directly to those in a position to use them. The program is developed on the basis of research needs identified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the Federal Highway Administration. Topics of the highest merit are selected by the AASHTO Special Committee on Research and Innovation (R&I), and each year R&Iâs recommendations are proposed to the AASHTO Board of Direc- tors and the National Academies. Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Academies and TRB. The needs for highway research are many, and NCHRP can make significant contributions to solving highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement, rather than to substitute for or duplicate, other highway research programs.
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CRP STAFF FOR NCHRP SYNTHESIS 537 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Tanya M. Zwahlen, Senior Program Officer Stephanie L. Campbell, Senior Program Assistant Eileen P. Delaney, Director of Publications Natalie Barnes, Associate Director of Publications NCHRP PROJECT 20-05 PANEL Joyce N. Taylor, Maine DOT, Augusta, ME (Chair) Socorro âCocoâ Briseno, California DOT, Sacramento, CA Anita K. Bush, Nevada DOT, Carson City, NV Joseph D. Crabtree, University of Kentucky, Lexington, KY Mostafa âMoeâ Jamshidi, Nebraska DOT, Lincoln, NE David M. Jared, Georgia DOT, Forest Park, GA Cynthia L. Jones, Ohio DOT, Columbus, OH Jessie X. Jones, Arkansas DOT, Little Rock, AR Brenda Moore, North Carolina DOT, Raleigh, NC Ben T. Orsbon, South Dakota DOT, Pierre, SD Randall R. âRandyâ Park, Avenue Consultants, Bluffdale, UT Jack Jernigan, FHWA Liaison Stephen F. Maher, TRB Liaison TOPIC 49-05 PANEL Lyndi D. Blackburn, Alabama DOT, Montgomery, AL Ram Bommavaram, California DOT, San Jose, CA John Garrity, Minnesota DOT, Maplewood, MN Timothy Kelley, Maine DOT, Augusta, ME Howard L. Moseley, Florida DOT, Gainesville, FL Roger C. Olson, Minnesota DOT, Bloomington, MN (retired) B. Shane Underwood, North Carolina State University, Raleigh, NC Matthew Corrigan, FHWA Liaison Jack Youtcheff, FHWA Liaison Nelson H. Gibson, TRB Liaison C O O P E R A T I V E R E S E A R C H P R O G R A M S
ABOUT THE NCHRP SYNTHESIS PROGRAM Highway administrators, engineers, and researchers often face problems for which information already exists, either in documented form or as undocumented experience and practice. This infor- mation may be fragmented, scattered, and unevaluated. As a consequence, full knowledge of what has been learned about a problem may not be brought to bear on its solution. Costly research findings may go unused, valuable experience may be overlooked, and due consideration may not be given to recommended practices for solving or alleviating the problem. There is information on nearly every subject of concern to highway administrators and engineers. Much of it derives from research or from the work of practitioners faced with problems in their day-to-day work. To provide a systematic means for assembling and evalu ating such useful informa- tion and to make it available to the entire highway community, the American Association of State Highway and Transportation Officialsâthrough the mechanism of the National Cooperative High- way Research Programâauthorized the Transportation Research Board to undertake a continuing study. This study, NCHRP Project 20-05, âSynthesis of Information Related to Highway Problems,â searches out and synthesizes useful knowledge from all available sources and prepares concise, docu- mented reports on specific topics. Reports from this endeavor constitute an NCHRP report series, Synthesis of Highway Practice. This synthesis series reports on current knowledge and practice, in a compact format, without the detailed directions usually found in handbooks or design manuals. Each report in the series provides a compendium of the best knowledge available on those measures found to be the most successful in resolving specific problems. FOREWORD By Tanya M. Zwahlen Staff Officer Transportation Research Board The objective of NCHRP Synthesis 537 is to document agency policy for lift thickness and mini- mum compaction requirements on resultant asphalt pavement quality. To achieve expected pave- ment performance, it is important that asphalt concrete (AC) have adequate density. A critical factor in achieving this density is the ratio of lift thickness to nominal maximum aggregate size (t/NMAS). The information in this report can help make agencies aware of a range of practices other agencies use to achieve a desired t/NMAS ratio, ensuring that density of AC is adequate to meet expected pavement performance. The information contained in this synthesis was obtained using three sources. First, a literature review was conducted on the state of practice of achieving desired lift thickness. Second, a survey was distributed to state departments of transportation as well as transportation agencies in Canadian provinces to determine their current mix type selection and pavement lift thickness standards and how they relate to structural design and construction specifications. Finally, follow-up interviews were conducted with agencies in selected states. Rebecca S. McDaniel of Purdue University collected and synthesized the information and wrote the report. The members of the topic panel are acknowledged on page iv. This synthesis is an imme- diately useful document that records the practices that were acceptable within the limitations of the knowledge available at the time of its preparation.
Note: Photographs, figures, and tables in this report may have been converted from color to grayscale for printing. The electronic version of the report (posted on the web at www.trb.org) retains the color versions. 1 Summary 3 Chapter 1 Introduction 4 1.1 Background 5 1.2 Synthesis Approach 6 Chapter 2 Literature Review: Effects of Lift Thickness on Pavement Performance 6 2.1 Basics of Compaction 8 2.2 Evolution of Superpave 11 2.3 Relationships Between Lift Thickness, NMAS, and Air Voids 13 2.4 Performance Impacts 19 2.5 Costs and Benefits 21 2.6 Summary of Findings from Literature 23 Chapter 3 Survey Results: Current Practices Regarding Lift Thicknesses 23 3.1 State DOT Survey Responses 34 3.2 Canadian Responses 35 3.3 Industry Survey Responses 43 3.4 Analysis and Summary of Survey Findings 44 Chapter 4 Case Examples 44 4.1 FloridaâThe Minerâs Canary? 46 4.2 Through Thick and Thin 48 4.3 Increasing Field DensityâA National Study 49 4.4 A Contractor Seeks Solutions 51 Chapter 5 Conclusions and Further Research 51 5.1 Conclusions 54 5.2 Gaps in the Knowledge and Future Research Needs 55 References 58 Abbreviations 60 Appendix A State Survey Questionnaire 67 Appendix B Industry Survey Questionnaire 72 Appendix C Tabulated State Survey Responses 103 Appendix D Tabulated Industry Survey Responses C O N T E N T S